Optical disk, optical disk device, and optical disk recording method

ABSTRACT

The present invention relates to an optical disk, an optical disk device, and an optical disk recording method. When it is applied to, for example, a compact disk. It attempts to reduce a jitter at the time of reproduction, and reproduce surely the recorded data. A change pattern of a modulation signal (S 2 ) is detected, and the timing of a modulation signal (S 1 ) is corrected according to this change pattern, to irradiate a laser beam L.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical disk, an optical diskdevice, and an optical disk recording method. The present invention isapplied to, for example, a compact disk. By correcting the timing of amodulation signal according to a change pattern of a modulation signal,a jitter at the time of reproduction is reduced and recorded data can besurely reproduced.

[0003] 2. Description of the Related Art

[0004] In a conventional compact disk, data to be recorded are subjectedto data processing and thereafter subjected to an EFM (Eight-to-FourteenModulation) modulation. For a predetermined fundamental period T, a pitsequence having a period in the range of 3T to 11T is thereby formed.Thereby, audio data or the like, for example, are recorded.

[0005] Corresponding to this, a compact disk player irradiates a laserbeam on the compact disk and receives a returned light therefrom. Thecompact disk player thus obtains a reproduced signal having a signallevel changed according to the light quantity of the returned light,converts this reproduced signal to a binary value by using apredetermined slice level, and thus generates a binary signal.Furthermore, the compact disk player drives a PLL circuit in response tothis binary signal to generate a reproduction clock and latches binarysignals successively by using the reproduction clock. Thereby, thecompact disk player generates reproduced data having a period in therange of 3T to 11T and corresponding to the pit sequence formed on thecompact disk.

[0006] The compact disk player conducts data processing corresponding tothe data processing conducted at the time of recording, on thereproduced data thus generated. In this way, the compact disk playerreproduces audio data or the like recorded on the compact disk.

[0007] By the way, in the conventional compact disk player, a jitter iscontained in the reproduced signal. It may be considered that thisjitter occurs by various causes such as a noise of a laser beam used forreadout, a thermal noise of an electric system, a disk noise or thelike. The jitter reduces the phase margin of the reproduced signal. Inan extreme case, the jitter makes it difficult to reproduce datacorrectly.

[0008] However, this jitter is essentially due to an inter-symbolinterference caused by preceding and succeeding pits (Shigeo Kubota,“Aplanatic condition required to reproduce jitter-free signals in anoptical digital disk system”, App. Optics 1987, Vol. 26, No. 18, pp.3961-3970). The jitter changes according to the land and pit locatedbefore and behind the laser beam radiation position.

SUMMARY OF THE INVENTION

[0009] In view of the points heretofore described, the present inventionhas been made. The present invention attempts to propose an opticaldisk, an optical disk device, and an optical disk recording methodcapable of reducing a jitter caused at the time of reproduction andreproducing surely the recorded data.

[0010] In order to solve the above described problems, in an opticaldevice and an optical disk recording method according to the presentinvention, the timing of a modulation signal is corrected according to achange pattern of the modulation signal.

[0011] Furthermore, in an optical disk, the position of an edge ischanged from its fundamental position according to the pit length andthe land length located before and behind the edge.

[0012] Furthermore, in an optical disk device and an optical diskrecording method, the timing at which a laser beam is raised up to alight quantity for writing is corrected in an interlinked relation tolight quantity switching of the writing operation.

[0013] Furthermore, in an optical disk, a high reflectance area and alow reflectance area are formed dependent on a difference in pit width.In order to correct a change of a returned light caused by thisdifference in pit width, pits to which the same data is assigned areformed so as to be different in pit length.

[0014] By correcting a timing of the modulation signal, a change causedin signal level at the time of reproduction can be corrected. If thistiming correction is executed on the basis of the change pattern of themodulation signal, a reproduced signal can be corrected so as to correctan inter-symbol interference changing according to this change pattern.As a result, the jitter of the reproduced signal can be reduced.

[0015] So as to correspond to this in an optical disk, the position ofan edge is changed from a fundamental position according to the pitlength and the land length located before and behind the edge to therebyform the pit. Whereby, the pit shape is changed so as to correspond tothe change pattern of the modulation signal. As a result, a jittercaused by inter-symbol interference can be avoided.

[0016] Furthermore, if the timing at which the laser beam is raised upto the light quantity for writing is corrected in an interlinkedrelation to light quantity switching of the writing operation, asymmetrychanged by light quantity switching can be corrected.

[0017] So as to correspond to this, in an optical disk, a highreflectance area and a low reflectance areas are formed dependent on adifference in pit width. Thereby, characters or the like can be recordedon the information recording surface so as to be observable with eyes.If at this time pits to which the same data is assigned are formed so asto be different in pit length so as to correct a change of a returnedlight caused by this difference in pit width, asymmetry differing in thehigh reflectance area and the low reflectance area can be corrected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a block diagram showing an optical disk device accordingto a first embodiment of the present invention.;

[0019]FIGS. 2A to 2E are each a signal waveform diagram used fordescription of the operation of an edge position correction circuitincluded in the optical disk device of FIG. 1;

[0020]FIG. 3 is a block diagram showing a rising edge correction circuitincluded in the optical disk device of FIG. 1;

[0021]FIG. 4 is a process diagram showing the production process of acorrection value table included in the optical disk device of FIG. 1;

[0022]FIG. 5 is a flow chart showing the processing procedure of acomputer in the process of FIG. 4;

[0023]FIG. 6 is a block diagram showing an optical disk device accordingto a second embodiment of the present invention;

[0024]FIG. 7 is a block diagram showing a character signal generationcircuit included in the optical disk device of FIG. 6;

[0025]FIG. 8 is a top view showing a compact disk produced by theoptical disk device of FIG. 6;

[0026]FIG. 9 is a signal waveform diagram showing a reproduced signal ofa portion of the compact disk using a light quantity of 100%;

[0027]FIG. 10 is a signal waveform diagram showing a reproduced signalof a portion of the compact disk using a light quantity of 85%;

[0028]FIG. 11 is a signal waveform diagram showing a change in slicelevel caused by a difference in light quantities; and

[0029]FIG. 12 is a signal waveform diagram showing a reproduced signalobtained from the compact disk of FIG. 8, in comparison with FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereafter, an optical disk, an optical disk device, and anoptical disk recording method according to embodiments of the presentinvention will be described by suitably referring to the accompanyingdrawings.

[0031] (1) First Embodiment

[0032]FIG. 1 is a block diagram showing an optical disk device accordingto an embodiment of the present invention. This optical disk device 1records audio data D1 output from a digital audio tape recorder 3 byexposing an original disk 2 to a light. In a manufacturing process of anoptical disk, this original disk 2 is subjected to development, and thensubjected to electroforming processing. Thereby, a mother disk isproduced. From this mother disk, a stamper is produced. Furthermore, inthe optical disk manufacturing process, a disk-like substrate isproduced from the stamper thus produced. By forming a reflective filmand a protective film on this disk-like substrate, a compact disk isproduced.

[0033] That is, in this optical disk device 1, a spindle motor 4 drivesand rotates the original disk 2. From an FG signal generator held at thebottom thereof, there is output an FG signal FG having a signal levelwhich rises up at every predetermined rotation angle. According to theexposure position of the original disk 2, a spindle servo circuit 5drives the spindle motor 4 so as to make the frequency of this FG signalequivalent to a predetermined frequency. As a result, the original disk2 is driven so as to be rotated under the condition of a constant linearvelocity.

[0034] A recording laser 7 is formed by a gas laser or the like, andemits a laser beam L for exposure of the original disk. A lightmodulator 8 is formed of an electro-acousto-optical element and effectson-off control on the laser beam L by using a modulation signal S1 toemits a resultant beam. A mirror 10 bends the optical path of this laserbeam L and emits a resultant beam toward the original disk 2. Anobjective lens 11 focuses the light reflected by the mirror 10 on theoriginal disk 2. The mirror 10 and the objective lens 11 aresuccessively moved in the radial direction of the original disk 2 insynchronism with the rotation of the original disk 2 by a sled mechanismwhich is not illustrated. As a result, the position of exposure to thelaser beam L is successively displaced in the outer peripheral directionof the original disk 2.

[0035] In such a state that the original disk 2 is driven and rotated inthis optical disk device 1, a track is formed so as to take a helicalshape by the movement of the mirror 10 and the objective lens 11, andpits are successively formed on this track so as to correspond to themodulation signal S1.

[0036] The audio data D1 is inputted from the digital audio taperecorder 3 to a modulation circuit 13. In addition, subcode datacorresponding to the audio data D1 is inputted to the modulation circuit13. The modulation circuit 13 conducts data processing on the audio dataD1 and the subcode data by using a data processing scheme stipulated fora compact disk. In other words, the modulation circuit 13 adds errorcorrection codes to the audio data D1 and the subcode data, thereafterconducts interleave processing thereto, subsequently conducts an EFMmodulation, and outputs an EFM signal S2.

[0037] An edge position correction circuit 14 detects a change patternof the EFM signal S2 and corrects the timing of the EFM signal S2 so asto effectively avoid the inter-symbol interference at the time ofreproduction according to this change pattern.

[0038] Specifically, in the edge position correction circuit 14, a levelconversion circuit 15 corrects the signal level of the EFM signal S2having an output amplitude value of 1 [V] to a TTL level having anoutput amplitude value of 5 [V]. A resulting signal is outputtedtherefrom. A PLL circuit 16 generates a clock CK (FIG. 2B) from the EFMsignal S2 (FIG. 2A), and outputs the clock CK. In the FFM signal S2, thesignal level changes with a period in the range of 3T to 11T for thefundamental period T. Therefore, the PLL circuit 16 thus generates theclock CK which changes in signal level according to the fundamentalperiod T synchronized to this EFM signal S2.

[0039] As shown in FIG. 3, a rising edge correction circuit 17A includesthirteen latch circuits 19A through 19M connected in series and operatedby the clock CK. An output signal S3 of the level conversion circuit 15is inputted to the series circuit of the latch circuits 19A to 19M. Therising edge correction circuit 17A samples the output signal S3 of thelevel conversion circuit 15 with the timing of the clock CK, and detectsthe change pattern of the EFM signal S2 on the basis of sampling resultsof thirteen consecutive points. Namely, in the case where a latch outputof, for example, “0001111000001” is obtained, it can be recognized as achange pattern containing pits of a length 4T continued after a space ofa length 5T. In the same way, in the case where a latch output of, forexample, “0011111000001” is obtained, it can be recognized as a changepattern containing pits of a length 5T continued after a space of alength 5T.

[0040] A correction value table 20 is formed of a read only memorystoring a plurality correction data. By using latch outputs of the latchcircuits 19A through 19M as an address, the correction value table 20outputs correction value data DF corresponding to the change pattern ofthe EFM signal S2. As an input, a monostable multivibrator (MM) 21receives the latch output of the latch circuit 19G located at the centerof thirteen latch circuits 19A to 19M connected in series. By using therising timing of this latch output as a reference, the monostablemultivibrator 21 outputs a rising pulse signal which is raised in signallevel for a predetermined interval of time (an interval sufficientlyshorter than the period 3T).

[0041] A delay circuit 22 has tap outputs of twelve stages. The delaytime difference between the respective taps is set equal to theresolution of timing correction of the modulation signal in the edgeposition correction circuit 14. The delay circuit 22 successively delaysthe rising pulse signal outputted from the monostable multivibrator 21and outputs the delayed signal from each tap. A selector 23 selects andoutputs a tap output of the delay circuit 22 according to the correctionvalue data DF. As a result, a rising pulse signal SS (FIG. 2(D)) changedin delay time according to the correction value data DF is selected andoutputted from the selector 23.

[0042] Thereby, the rising edge correction circuit 17A generates therising edge signal SS which rises in signal level in response to eachrising of the signal level of the EFM signal S2. The delay time of eachrising edge with respect to the EFM signal S2, such as Δr(3, 3), Δr(4,3), Δ(3, 4), Δr(5, 3), . . . is changed according to the change patternof the EFM signal S2 detected by the corresponding rising edges of theEFM signal S2, i.e., by thirteen sampling operations before and after intotal.

[0043] In FIG. 3, the change pattern of the modulation signal S2 isrepresented by a pit length p and a pit interval b while taking oneperiod of the clock (i.e., channel clock) CK as the unit. The delay timefrom the rising edge is represented by Δr(p, b). In FIG. 2D, therefore,the second delay time Δr(4, 3) is the delay time in the case where ablank of three clocks precedes a pit having a length of four clocks. Inthe correction value table 20, correction value data DF corresponding toall combinations of p and b are stored beforehand.

[0044] In general, the compact disk is exposed to the laser beam Laccording to the EFM signal S2 and pits are thus formed thereon. For therange of 12T where the fundamental period T is taken as the unit, therising edge correction circuit 17A detects the pattern of pits formed onthe compact disk, and generates the rising edge signal SS according tothis pattern.

[0045] A falling edge correction circuit 17B has the same configurationas the rising edge correction circuit 17A except that the monostablemultivibrator 21 is operated on the basis of the falling edge of thelatch output and contents of the correction value table 20 aredifferent.

[0046] Thereby, the falling edge correction circuit 17B generates afalling edge signal SR (FIG. 2C) which rises in signal level in responseto each falling of the signal level of the EFM signal S2. The delay timeof each falling edge with respect to the EFM signal S2, such as Δf(3,3),Δf(4,4), Δf(3,3), Δf(5,4), . . . is changed according to the changepattern of the EFM signal S2 detected by the corresponding falling edgesof the EFM signal S2, i.e., by thirteen sampling operations in total. InFIG. 3, the delay time from each falling edge is represented by Δf(p, b)by using the pit length p and the pit space b in the same way as thedelay time for a rising edge.

[0047] For the range of 12T where the fundamental period T is taken asthe unit, the falling edge correction circuit 17B detects the pattern ofpits formed on the compact disk, corrects the timing of a falling edgeof the EFM signal S2 functioning as the timing of termination ofexposure to the laser beam according to the pattern, and generates thefalling edge signal SR.

[0048] A flip-flop (F/F) 25 (FIG. 1) combines the rising edge signal SSand the falling edge signal SR, and outputs a resultant signal. In otherwords, the rising edge signal SS and the falling edge signal SR areinput to a set terminal S and a reset terminal R of the flip-flop 25,respectively. As a result, the flip-flop 25 generates a modulationsignal S5 which rises in signal level in response to each rising edge ofthe signal level of the rising edge signal SS and which then falls insignal level in response to each rising edge of the signal level of thefalling edge signal SR. A level inverse conversion circuit 26 correctsthe signal level of this modulation signal S5 having an output amplitudeof a TTL level, and outputs it with the original output amplitude of 1V.

[0049] As a result, the modulation signal S1 is outputted with thetiming of the rising edge and the falling edge corrected according tothe pit length and land length located before and behind. Correspondingto this, the timing of exposure of the original disk 2 to the laser beamL is also corrected according to the pit length and land length locatedbefore and behind. In the compact disk produced by this original disk 2,therefore, each edge position is changed from its fundamental positionaccording to the pit length and land length located before and behind.As a result, between pits having the same data allocated thereto, thepit length is changed. Thereby, the optical disk device 1 corrects thepositions of the front edge and the rear edge of each pit at the time ofreproduction so as to reduce the jitter caused by the inter-symbolinterference.

[0050]FIG. 4 is a process diagram for the explanation of the generationof the correction value table 20 thus used to correct the edge timing.By suitably setting this correction value table 20 in the optical diskdevice 1, positions of the front edge and the rear edge of each pit canbe set to optimum positions, and reproduced signals can be changedaccording to correct timing synchronized to the clock CK. specifically,even if the pit size and lengths of the preceding and succeeding blankschange, reproduced signals thus pass through a predetermined slice levelat correct timing synchronized to the clock CK. As a result, reproducedsignals reduced in jitter can be obtained. The correction value table 20is present in both the rising edge correction circuit 17A and thefalling edge correction circuit 17B. Its setting method is the same forboth of them. Therefore, explanation will now be limited to the risingedge correction circuit 17A.

[0051] In this process, a correction value table is set on an originaldisk for evaluation by the optical disk device 1 on the basis of theresult of reproduction of a compact disk produced from this originaldisk.

[0052] When this original disk for evaluation is produced, thecorrection value table 20 for evaluation reference is set in the opticaldisk device 1. In this correction value table 20 for evaluationreference, the correction value data DF is set so as to always selectand output the center tap output of the delay circuit 22 by the selector23. In this process, therefore, the original disk 2 is exposed to lightunder the same condition as in the case where the light modulator 8 isdriven directly by the EFM signal S3, i.e., under the same condition asthe conventional compact disk producing process.

[0053] In this process, the original disk 2 thus exposed to light issubjected to development, and then subjected to electroformingprocessing. Thereby, a mother disk is produced. From this mother disk, astamper 40 is produced. Furthermore, in the same way as the conventionalcompact disk producing process, a compact disk 41 is produced from thestamper 40.

[0054] A compact disk player (CD player) 42 conducts reproductionoperation for the compact disk 41 for evaluation thus produced. At thistime, the compact disk player 42 switches its operation under thecontrol of a computer 44, and outputs a reproduced signal RF from itsinternal signal processing circuit to a digital oscilloscope 43. Thisreproduced signal RF has a signal level changed according to the lightquantity of the returned light which is obtained from the compact diskand is output from an output of an optical pickup via a predeterminedbuffer circuit. Thus, this compact disk 41 is produced under the samecondition as the usual compact disk. If this reproduced signal RF isobserved on the digital oscilloscope 43 by using the reproduced clock asa trigger, therefore, a jitter can be observed.

[0055] The digital oscilloscope 43 switches its operation under thecontrol of the computer 44, conducts analog-digital conversion on thereproduced signal RF with a sampling frequency which is 20 times as highas the frequency of the channel clock, and outputs a resultant digitalsignal to the computer 44.

[0056] In addition to controlling the operation of the digitaloscilloscope 43, the computer 44 conducts signal processing on thedigital signal output from the digital oscilloscope 43, and therebysuccessively calculates the correction value data DF. Furthermore, thecomputer 44 drives a ROM writer 45 to store the calculated correctionvalue data DF successively in a read only memory, and thereby forms thecorrection value table 20. In this process, a compact disk is finallymanufactured by using this correction value table 20.

[0057]FIG. 5 is a flow chart showing the processing procedure in thecomputer 44. In this processing procedure, the computer 44 proceeds fromstep SP1 to step SP2, and sets a jitter detection result Δr(p,b) and thenumber of times of jitter measurement n(p,b) equal to values 0. Aroundeach edge which is the subject of jitter detection, the computer 44calculates the jitter detection result Δr(p,b) for each combination ofthe pit length p and the pit interval b, and counts the number of timesof jitter measurement n(p,b). At step SP2, therefore, the computer 44sets all of the jitter detection result Δr(p,b) and the number of timesof jitter measurement n(p,b) equal to initial values.

[0058] Subsequently, the computer 44 proceeds to step SP3. By comparingthe digital signal output from the digital oscilloscope 43 with apredetermined slice level, the computer converts the reproduced signalRF to a binary value and thus generates a digital binary signal. In thisprocessing, the computer 44 converts the digital signal to a binaryvalue so as to provide a digital signal of the slice level or higherwith a value 1 and provide a digital signal of less than the slice levelwith a value 0.

[0059] Subsequently, the computer 44 proceeds to step SP4, and generatesa reproduced clock from a binary signal formed digital signal. Here, thecomputer 44 simulates the operation of the PLL circuit by conductingcomputation processing on the basis of the binary signal, and therebygenerates the reproduced clock.

[0060] In subsequent step SP5, the computer 44 samples the binary signalat timing of each falling edge of the reproduced clock thus generated,and thereby decodes the EFM signal. (Hereafter, this EFM signal thusdecoded is referred to as a decoded EFM signal.)

[0061] Subsequently, the computer 44 proceeds to step SP6, and detects atime difference e measured from the time point of a rising edge of thebinary signal to the time point of a falling edge of the reproducedclock closest to the former cited falling edge. Thereby, the computer 44measures the time of jitter at this edge. Subsequently at step SP7, thecomputer 44 detects the preceding and succeeding pit length p and pitinterval b from the decoded EFM signal for the edge the time of whichhas been measured at the step SP6.

[0062] Subsequently at step SP8, the computer 44 adds the timedifference e detected at the step SP6 to the jitter detection resultΔr(p,b) corresponding to the preceding and succeeding pit length p andpit interval b, and increases the corresponding number of times ofjitter measurement n(p,b) by a value of 1. Subsequently, the computer 44proceeds to step SP9, and determines whether or not the timemeasurements for all rising edges have been completed. If a negativeresult is obtained here, the computer returns to the step SP5.

[0063] As a result, the computer 44 repeats the processing procedure ofsteps SP5-SP6-SP7-SP8-SP9-SP5, accumulates the jitter detection resultsmeasured for time every change pattern appearing in the reproducedsignal RF, and counts the number of additions.

[0064] If jitter time measurements for all edges have thus beencompleted, an affirmative result is obtained at the step SP9. As aresult, the computer 44 proceeds to step SP10. For each change patternappearing in the reproduced signal RF, the computer averages the jitterdetection results measured for time. Namely, the jitter detected at thestep SP6 is influenced by a noise. By thus averaging the jitterdetection results, the computer 44 improves the precision of jittermeasurement.

[0065] Upon thus averaging the jitter detection results, the computer 44subsequently proceeds to step SP11. On the basis of the detectionresult, the computer generates the correction value data DF for eachchange pattern and outputs each correction value data DF to the ROMwriter 45. Denoting the delay time difference between taps in the delaycircuit 22 by τ, this correction value data DF is calculated byexecuting the computation processing of the following equation (1).$\begin{matrix}{{{Hr1}\left( {p,b} \right)} = {\frac{{{- a} \cdot \Delta}\quad {r\left( {p,b} \right)}}{\tau} + {{Hr0}\left( {p,b} \right)}}} & (1)\end{matrix}$

[0066] Here, Hr1(p,b) denotes a tap of the delay circuit 22 selected bythe correction value data DF. In case of the value 0, the center tap isrepresented. Furthermore, Hr0(p,b) denotes a tap of the delay circuit 22selected by the correction value data DF which is the initial value. Inthis embodiment, Hr0(p, b) is preset to 0. Furthermore, “a” is aconstant. In this embodiment, “a” is set to a value of 1 or less (forexample, such as 0.7 or the like). Multiplication is conducted so as tobe capable of making the correction value surely converge even if thereis an influence of a noise or the like.

[0067] Upon thus storing the correction value data DF in the ROM writer45, the computer 44 proceeds to step SP12 and terminates this processingprocedure. Subsequently, the computer 44 executes a similar processingprocedure for falling edges of the digital binary signal, and therebycompletes the correction value table 20.

[0068] In the configuration heretofore described, the correction valuetables 20 in the rising edge correction circuit 17A and the falling edgecorrection circuit 17B included in the optical disk device 1 (FIG. 1)are set equal to initial values. Under the same condition as theproduction condition of the conventional disk, the original disk 2 forevaluation is produced (FIG. 4). From this original disk 2, the compactdisk 41 for evaluation is produced.

[0069] In the compact disk 41 for evaluation, by the EFM signal changingin signal level with a period equivalent to an integer multiple of thefundamental period T, the laser beam L is subjected to on-off control.The original disk 2 is successively exposed to light, and pits areformed. In the compact disk 41 for evaluation, therefore, the reproducedsignal undergoes inter-symbol interference from the adjacent pit andland. Therefore, the timing at which the reproduced signal obtained fromthis compact disk 41 crosses the slice level changes according to theshape of the pit and land located before and behind, i.e., according tothe change pattern of the EFM signal. Thus, a jitter occurs.

[0070] This compact disk 41 undergoes the reproduction operationconducted by the compact disk player 42. The reproduced signal RF isconverted to a digital signal by the digital oscilloscope 43.Thereafter, the binary signal, the decoded EFM signal, and thereproduced clock are generated by the computer 44. Furthermore, for eachedge of the binary signal from the compact disk 41, the pit and landlocated before and after are detected from the decoded EFM signal, andthe change pattern of the EFM signal is detected. For each changepattern, the jitter quantity of each edge for the reproduced clock ismeasured in the form of time.

[0071] Furthermore, these time measurement results are averaged for eachchange pattern. The jitter quantity caused by the inter-symbolinterference is detected for each change pattern. By using the jitterquantity thus detected, the compact disk 41 executes the computationprocessing of the equation (1), which is based on the delay timedifference τ between taps of the delay circuit 22 (FIG. 3) and whichincludes the jitter correction unit. By taking the center tap of thedelay circuit 22 as the reference, the tap position of the delay circuit22 capable of canceling the detected jitter quantity is detected. Thedata specifying this tap position is stored in the read only memory asthe correction value data DF. As a result, the correction value table 20is formed.

[0072] By thus forming the correction value table 20, the audio data D1and subcode data input from the digital audio tape recorder 3 (FIG. 1)are subjected to stipulated data processing in the modulation circuit 13and converted to the EFM signal S2, which changes in signal level whiletaking the fundamental period T as the unit. This EFM signal S2 isconverted in signal level to the TTL level by the level conversioncircuit 15. Thereafter, the clock CK is reproduced by the PLL circuit16. In the rising edge correction circuit 17A and the falling edgecorrection circuit 17B (FIG. 3), the signal is successively latched inthe 13-stage latch circuits 19A through 19M, and the change pattern isdetected.

[0073] Furthermore, the EFM signal S2 is input from the latch circuitlocated at the middle of the latch circuits 19A through 19M to themonostable multivibrator 21. The monostable multivibrator 21 istriggered at the timing of the rising edge in the rising edge correctioncircuit 17A and at the timing of the falling edge in the falling edgecorrection circuit 17B. In the rising edge correction circuit 17A andthe falling edge correction circuit 17B, the rising pulse signal and thefalling pulse signal which rise in signal level respectively at thetiming of the rising edge and the falling edge are generated,respectively.

[0074] Respectively in the delay circuits 22 of the rising edgecorrection circuit 17A and the falling edge correction circuit 17B, therising pulse signal and the falling pulse signal are successivelydelayed while taking the delay time τ used to calculate the correctionvalue data DF as the unit. Tap outputs of this delay circuit 22 areoutput to the selector 23. As for the change pattern of the EFM signalS2 detected by the latch circuits 19A through 19M, accessing thecorrection value table 20 by using the latch outputs of the latchcircuits 19A through 19M yields detection of the correspondingcorrection value data DF. By this correction value data DF, contacts ofthe selector 23 are switched.

[0075] Respectively from the selectors 23 of the rising edge correctioncircuit 17A and the falling edge correction circuit 17B, the rising edgesignal SS and the falling edge signal SR respectively corrected intiming of the rising edge and the falling edge of the EFM signal S2 soas to correct the jitter detected in the compact disk 41 for evaluationare output. The rising edge signal SS and the falling edge signal SR(FIG. 1) are combined by the flip-flop 25. The output signal S5 of theflip-flop 25 is corrected in signal level by the inverse levelconversion circuit 26. As a result, the modulation signal S1 correctedin timing of each edge of the EFM signal S2 so as to correct the jitterdetected on the compact disk 41 for evaluation, i.e., so as to reducethe inter-symbol interference is generated. By this modulation signalS1, exposure of the original disk 2 is conducted.

[0076] As a result, pits are formed successively on the original disk 2with edge positions corrected so as to cancel the inter-symbolinterference. From this original disk 2, a compact disk significantlyreduced in jitter as compared with the conventional compact disk isproduced.

[0077] In the configuration heretofore described, the modulation signalS1 is generated by correcting the timing of the EFM signal S2 accordingto the change pattern of the EFM signal S2, and the original disk 2 isexposed to light by using this modulation signal S1. As a result, thejitter caused by the inter-symbol interference changing according to thechange pattern can be reduced significantly as compared with theconventional compact disk.

[0078] Furthermore, at this time, the compact disk for evaluation isproduced and the correction value data DF is generated. Therefore, evenif the production condition of the compact disk has changed, the compactdisk can be produced by means of always proper correction value data DFby newly deriving the correction value data DF.

[0079] (2) Second Embodiment

[0080]FIG. 6 is a block diagram showing an optical disk device accordingto a second embodiment of the present invention. In this optical diskdevice 50, the light quantity of the laser beam L is made to rise at apredetermined timing, and the original disk 2 is exposed to the light.Thereby, a pit widened in width is locally formed, and the reflectanceof the compact disk is locally changed. So as to make a character, animage, and the like observable and confirmable with eyes by this localchange of reflectance, the character, the image and the like arerecorded on the information recording surface of the compact disk inthis optical disk device 50. In the components shown in FIG. 6, the samecomponents as those of the optical disk device 1 described before withreference to the first embodiment are denoted by corresponding referencenumerals and duplicated description thereof will be omitted.

[0081] That is, in this optical disk device 50, a character signalgeneration circuit 51 outputs a light quantity switching signal SC1,drives a light modulator 52 inserted in the optical path of the laserbeam L, and thereby switches and controls the light quantity of thelaser beam L.

[0082] In the character signal generation circuit 51, as shown in FIG.7, a counter modulo N 53 is formed by a ring counter, counts the FGsignal FG, and outputs a count value CT1. At a rotation period of thespindle motor 4, the count value is switched to 0. At this time, a tracksignal C1 is output.

[0083] A counter modulo M 54 is formed by a counter modulo M countingthe track signal C1, and outputs a count value CT2. By using the countermodulo N 53 and the counter modulo M 54, the character signal generationcircuit 51 outputs the count values CT1 and CT2, which respectivelyrepresent positions of the original disk 2 in the circumferentialdirection and in the radial direction.

[0084] A character signal generation table 55 is formed by a read onlymemory circuit which holds pixel values of various kinds of characterinformation. By using the count values CT1 and CT2 as an address, thecharacter signal generation table 55 outputs data of each pixel value.The data of each pixel value is formed by data of each bit whichrepresents, in a bit map form, the characters and image to be recordedon the original disk 2.

[0085] A level conversion circuit 56 successively latches the data ofpixel values successively input, and outputs them with a signal levelsuitable for driving the light modulator 52 (FIG. 6). In thisembodiment, the light modulator 52 is thus driven to switch the lightquantity of the laser beam L from the light quantity of 100% to thelight quantity of 85%. As a result, the characters, image and the likeare recorded on the surface of the disk as shown in FIG. 8.

[0086] If the light quantity of the laser beam L is thus controlled tobe switched from the light quantity of 100% to the light quantity of85%, the reproduced signal also changes. To be concrete, amplitude W1and W2 of the reproduced signal change as shown in FIGS. 9 and 10respectively illustrating eye patterns of the reproduced signals usingthe light quantity of 100% and the light quantity of 85% as shown inFIG. 11. If it is observed as a continuous waveform, a slice level SL1for correctly converting the reproduced signal to a binary value in thecase of the light quantity of 100% is different from a slice level SL2for correctly converting the reproduced signal to a binary value in thecase of the light quantity of 85%. In other words, asymmetry in theportion obtained with the light quantity of 100% changes largely fromthat in the portion obtained with the light quantity of 85%.

[0087] Conventional compact disk players have an automatic slice leveladjusting circuit for correcting the slice level according to such achange in asymmetry. If the light quantity of the laser beam L isabruptly changed to emphasize the contour so as to make the recordedcharacters, image and the like clearly observable and confirmable witheyes, however, it eventually becomes difficult for the automatic slicelevel adjusting circuit to follow such an abrupt change. In the boundaryportions of the characters, image and the like, therefore, very longburst errors occur.

[0088] In this embodiment, therefore, modulation signals S1A and S1Brespectively corresponding to the light quantities of 100% and 85% areoutput from two edge correction circuits 57A and 57B. The modulationsignal S1A or S1B is selected by a data selector 58 in an interlinkedrelation to the switching of the light quantity of the laser beam L.

[0089] Thus, in the optical disk device 50, the light quantity of thelaser beam L is switched over, and the modulation signal S1A or S1B isselected to vary the timing of exposure to the laser beam according tothe pit width thus changed. As a result, the edge position in each pitis varied so as to correspond to the change of the pit width. In thecompact disk produced by this original disk 2, pits to which the samedata is allocated are formed to be different in pit length so as tocorrect a change in the returned light caused by a difference in pitwidth.

[0090] At this time, the degree of the inter-symbol interference forrespective light quantities also changes due to a change in pit width.According to the change pattern of the EFM signal S2, therefore, timingsof the modulation signals S1A and S1B are varied by the edge positioncorrection circuits 57A and 57B, respectively. As a result, the jitteris reduced. Thus, the edge position correction circuits 57A and 57B holdthe correction value data DF respectively produced by the lightquantities of 100% and 85% in the correction value table.

[0091] As shown in FIG. 12 illustrating a result observed in anexperiment, the change of asymmetry could be effectively avoided byswitching over the timing of the modulation signal. With a slice levelSL, therefore, the reproduced signal obtained from the light quantity of100% and the reproduced signal obtained from the light quantity of 85%could be accurately converted to a binary value.

[0092] In the configuration shown in FIG. 6, the modulation signal S1Aand S1B are switched over by the data selector 58 to switch over thetiming of the modulation signal in an interlinked relation to theswitching of the light quantity of the laser beam. As a result, thereproduced signal can be accurately converted to a binary value by usinga single slice level. Accordingly, errors can be effectively avoided anddata can be reproduced precisely.

[0093] (3) Other Embodiments

[0094] In the above described embodiments, the case where the correctionvalue table produced by using the compact disk for evaluation isdirectly used to produce a compact disk has been described. However, thepresent invention is not limited to this, but by using the correctionvalue table produced by means of the compact disk for evaluation, acompact disk for evaluation may be newly produced so as to modify thecorrection value table by using the newly produced compact disk forevaluation. If the correction value table is thus modified repeatedly,the jitter can be reduced positively by that amount.

[0095] In the above described embodiments, the case where the EFM signalis sampled 13 times to detect the change pattern has been described.However, the present invention is not limited to this, but the number ofsampling points may be increased, if necessary, to thereby cope with alonger recording information pattern.

[0096] In the above described embodiments, the case where the jitterquantity is measured by measuring the time of the binary signal basedupon the fundamental clock and the correction value data are generatedfrom the measurement results has been described. However, the presentinvention is not limited to this. In the case where a practicallysufficient precision can be assured, the correction value data may begenerated by signal level detection of the reproduced signal based uponthe fundamental clock instead of the measurement of the jitter quantityusing this time measurement. In this case, error voltage from thedetected signal level of the reproduced signal the slice level iscalculated, and correction value data is calculated from the errorvoltage and the transient response characteristic of the reproducedsignal.

[0097] In the above described embodiments, the case where the timing ofthe modulation signal is corrected according to the correction valuedata stored in a table form has been described. However, the presentinvention is not limited to this. In the case where a practicallysufficient precision can be assured, the correction value data may becalculated by computation processing instead of the correction valuedata detected beforehand and the timing of the modulation signal may becorrected by using the correction value data thus calculated.

[0098] In the above described embodiments, the case where the correctionvalue data is calculated by using the compact disk for evaluation hasbeen described. However, the present invention is not limited to this.In the case where the present invention is applied to, for example, anoptical disk device of a write-once type, the correction value data maybe calculated on the basis of trial writing result in a so-called trialwriting area.

[0099] In the above described embodiments, the case where the presentinvention is applied to the compact disk has been described. However,the present invention is not limited to this, but the present inventioncan be widely applied to optical disk devices for recording various databy using pits. The present invention can be widely applied to opticaldisk devices adapted to conduct multi-value recording of various data bydifference in transient response characteristics of the reproducedsignal.

[0100] In accordance with the present invention, the timing of themodulation signal is corrected according to the change pattern of themodulation signal as described above. As a result, the jitter caused bythe inter-symbol interference can be reduced. The reading margin can beimproved by that amount, and recorded data can be reproduced surely.

[0101] Furthermore, in an interlinked relation to the switching over ofthe light quantity of the laser beam, the timing of the modulationsignal is corrected. Thereby, asymmetry is corrected, and data can bereproduced accurately with a single slice level. Furthermore,degradation of jitter caused by the light quantity switching over of thelaser beam can be effectively avoided. From these facts, it becomespossible to record an image, a character and the like, and surelyreproduce recorded data.

[0102] Having described preferred embodiments of the present inventionwith reference to the accompanying drawings, it is to be understood thatthe present invention is not limited to the above-mentioned embodimentsand that various changes and modifications can be effected therein byone skilled in the art without departing from the spirit or scope of thepresent invention as defined in the appended claims.

What is claimed is:
 1. An optical disk device for switching a signallevel of a modulation signal at a period equivalent to an integermultiple of a predetermined fundamental period according to data to berecorded, conducting on-off control on a laser beam by using saidmodulation signal, and thereby recording said data on a disk-likerecording medium, comprising: a change pattern detection means fordetecting a change pattern of said modulation signal by sampling saidmodulation signal at said fundamental period; and a timing correctionmeans for correcting a timing of said modulation signal according tosaid change pattern, wherein said timing correction means corrects thetiming of said modulation signal so that a binary signal will changewhile taking said fundamental period as unit when a reproduced signalobtained from said disk-like recording medium is converted to saidbinary signal with a predetermined slice level.
 2. An optical diskdevice according to claim 1 , wherein said timing correction meanscorrects the timing of said modulation signal according to correctiondata stored in correction data storing means and said correction data isset on the basis of a result of reproduction of a disk-like recordingmedium for evaluation.
 3. An optical disk recording method for switchinga signal level of a modulation signal at a period equivalent to aninteger multiple of a predetermined fundamental period according to datato be recorded, conducting on-off control on a laser beam by using saidmodulation signal, and thereby recording said data on a disk-likerecording medium, comprising the step of: correcting a timing of saidmodulation signal according to a change pattern of said modulationsignal.
 4. An optical disk recording method according to claim 3 ,wherein predetermined data are recorded on a separate disk-likerecording medium and a reproduction result is obtained, or said data arerecorded on said disk-like recording medium and a reproduction result isobtained, and the timing of said modulation signal is corrected on thebasis of said reproduction result.
 5. An optical disk recording methodaccording to claim 4 , wherein a reproduced signal obtained byreproducing said disk-like recording medium is converted to a binarysignal with a predetermined slice level, wherein a timing of an edge ofsaid binary signal for said fundamental period is detected whenever saidchange pattern occurs, and wherein said reproduction result comprises sresult of said detection.
 6. An optical disk having desired datarecorded thereon by a pit formed on an information recording surface,wherein said pit is formed so that a position of each edge will bechanged from a fundamental position according to a pit length and a landlength located before and behind said edge.
 7. An optical disk devicefor generating a modulation signal according to data to be recorded,driving a laser light source by using said modulation signal tointermittently raise a light quantity of a laser beam to a lightquantity for writing, and recording said data on a disk-like recordingmedium, comprising: a light quantity switching means for switching oversaid light quantity for writing; and a timing control means for varyinga timing of said modulation signal in an interlinked relation to saidlight quantity switching means and thereby correcting a timing ofraising the light quantity of said laser beam to said light quantity forwriting.
 8. An optical disk device according to claim 7 , wherein saidtiming control means comprises a change pattern detection means fordetecting a change pattern of said modulation signal by successivelysampling said modulation signal at a clock timing synchronized to saiddata, and a timing correction means for correcting the timing of saidmodulation signal according to said change pattern.
 9. An optical diskdevice according to claim 8 , wherein said timing correction meanscorrects the timing of said modulation signal according to correctiondata stored in correction data storing means, and said correction datais set beforehand on the basis of a result of reproduction of adisk-like recording medium for evaluation.
 10. An optical disk recordingmethod for intermittently raising a light quantity of a laser beam to alight quantity for writing according to data to be recorded, andrecording said data on a disk-like recording medium, comprising the stepof: increasing, in a predetermined area of said disk-like recordingmedium, said light quantity for writing; and correcting a timing ofraising the light quantity of said laser beam to said light quantity forwriting in response to said increase of said light quantity for writing.11. An optical disk having desired data recorded thereon by a pit formedon an information recording surface, comprising: an area having a highreflectance value and an area having a low reflectance value formed onsaid information recording surface; and a desired image recorded on saidinformation recording surface thereby, wherein said high reflectancearea and said low reflectance area are formed dependent on a differencein pit width of said pit; and said pit is formed so that pit to whichthe same data is allocated has a different pit length in order tocorrect a change of a returned light caused by said difference in pitwidth at time of reproduction.